Add support for Youtube meta tags with itemprop attributes

[mworrell]

This pull request improves the extraction and handling of HTML metadata, specifically by adding support for the itemprop attribute in <meta> tags. This allows the system to better parse and map structured metadata, such as those used by YouTube and other platforms that leverage schema.org properties. Additionally, new tests are included to ensure the correct extraction of these properties.

Enhancements to HTML metadata extraction:

• Added support for parsing the itemprop attribute in <meta> tags, enabling extraction of structured metadata fields such as name, description, and thumbnailUrl.
• Introduced the meta_itemprop_tag/3 function to handle mapping of specific itemprop values (name to title, thumbnailUrl to thumbnail) and fallback for other values.

Testing improvements:

• Added a new test (youtube_itemprop_html_meta_test) to verify correct extraction of YouTube-style itemprop metadata, including title, description, and thumbnail URL.

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